1. Field of the Invention
This invention relates generally to hydraulic tools. In particular, this invention relates to a rock drill in which seawater is used as the hydraulic fluid.
2. Description of the Prior Art
Prior art hydraulic rock drills designed for underwater usage have typically employed oil as the hydraulic fluid. The hydraulic fluid is pumped from a surface ship through a supply hose down to the diver, and must be returned to the surface ship via a return hose. The need for such supply and return hoses limits the diver's handling of the rock drill, particularly where heavy surge and strong currents exist. The use of oil as the hydraulic fluid creates logistics problems in requiring shipping and storage of large quantities of oil. Leakage of the oil fluid from the rock drill contaminates the environment, and leakage of seawater into the rock drill readily damages the precision rock drill components.
There are a variety of prior art rock drills which use oil as the working pressurized fluid. For example, U.S. Pat. No. 4,157,121 discloses a rock drill having a piston hammer which is arranged to impact on an anvil in the form of a chisel which extends out of a housing and which uses oil as the working fluid. U.S. Pat. Nos. 4,676,323 and 3,945,442 illustrate other examples of prior art rock drills which use oil as the working fluid.
The design of a hydraulic rock drill which utilizes seawater as the hydraulic fluid presents a serious challenge to the designer because of the general corrosiveness of seawater on precision made parts used in such rock drills. The poor lubricity of seawater and a much lower viscosity for seawater than for conventional oil hydraulic fluid contribute to the problem. The generally lower viscosity which seawater exhibits means that all design clearances should be an order of magnitude less than for prior art oil hydraulic fluid rock drills.
With these and other disadvantages known to oil hydraulic fluid rock drills, the present invention was conceived and one of its objectives is to provide a rock drill which utilizes seawater as the operating fluid and provides satisfactory results for the user.
It is another object of the present invention to provide a rock drill designed such that seawater acts as the lubricant for wear surfaces.
It is still another object of the present invention to provide a rock drill which utilizes seawater as the hydraulic fluid so as not to contaminate the environment.
Various other advantages and objectives of the present invention will become apparent to those skilled in the art as a more detailed description of the invention is set forth below.